1. Field of the Invention
The present invention relates to a communication apparatus and control method therefor.
2. Description of the Related Art
Conventionally, communication apparatuses such as facsimile (FAX) apparatuses are available which can connect, to a communication line such as a telephone line, not only a FAX communication unit for a FAX communication (modem) but also a telephone for a voice communication. For example, Japanese Patent Laid-Open No. 05-007273 discloses a FAX apparatus which can selectively connect a data communication unit used to make a data communication and a telephone used to make a voice communication to a communication line. When this FAX apparatus switches the data communication unit to the telephone and connects it to the communication line, the data communication unit and telephone are connected to the communication line in parallel to each other, so as to supply a line current to the telephone, thereby setting the telephone in a voice communication ready state before switching connection to it.
Some of such conventional FAX apparatuses are connected to a public branch exchange (PBX), but most of them are connected to a public switched telephone network (PSTN). Strict managements are made for FAX apparatuses connected to the PSTN and apparatuses introduced as switching equipments on the PSTN side, so that these apparatuses meet predetermined technical criteria.
On the other hand, a technique called “VoIP” (Voice over Internet Protocol) which exchanges voice data using an IP network having a broadband transmission path such as a Digital Subscriber Line (DSL) or optical line has prevailed.
When the user connects the aforementioned communication apparatus for the PSTN (a FAX apparatus will be exemplified below) to the IP network, and makes a voice communication by a telephone connected to the communication apparatus using the VoIP, he or she encounters the following problem. For example, an adapter which serves as an interface used to convert a voice signal output from the apparatus into a signal having a format suited to the IP network is required. This adapter normally not only sends the input voice signal onto the IP network, but also specifies a communication destination by detecting an input dial pulse signal.
Since the adapter connected to the FAX apparatus is not connected to the PSTN, it is not required to meet the predetermined technical criteria required for the PSTN connection. For this reason, such adapter may often erroneously detect, as a dial pulse signal, a weak current or voltage change having a short time width at a level as low as it cannot be detected as a regular dial pulse signal according to the criteria for the PSTN.
More specifically, in the communication apparatus, a weak current or voltage change having a very short time width, which is caused upon switching of an internal relay or an off-hook operation of the externally attached telephone, may often be erroneously detected by the aforementioned adapter as a dial pulse signal. In this case, the apparatus cannot dial to a correct destination based on the dial pulse signal from the telephone.